Useful information, and thanks for the diagram. The next question is "is it worth fixing?" The $450 rough estimate is rather steep, and I can live with the two-minutes of noise. What is the downside to not addressing this particular venting problem? It does not seem to be an issue elsewhere in the house.

Thanks,

- Neal

: Neal,: It does sound like a venting problem. I don't know whether it could be fixed from the roof or not. You may not even have a vent attached to the drain. The glug-glug sounds like water siphoning out of the trap. Terry